Data source connection string maintains in connection file (rds).It can be reusable for multiple reports in the application.

In SSAS and SSIS2008 we have only shared Data source.

Dataset:

Dataset means in-memory result set structure prepared based on query or stored procedure.
Dataset populated with actual rows at the time of report execution.

A report requires at least one dataset.
A report can use multiple datasets.

List:
A list data region repeats with each group or row in the report dataset.
•List region does not have any built -in – layout.
•It’s free from layout.
•List can display detailed data and aggregated data with the help of other report items.
•List can support only one grouping that is on entire list.
•A report item placed in the list can be repeated from each row in the dataset/each group in the dataset.